Once a measure steers behaviour, it changes from an observation tool into part of the system.
The popular slogan “when a measure becomes a target…” is broader than Goodhart’s original warning. Goodhart addressed unstable statistical relationships under policy control; Campbell emphasised corruption pressure and distortion when indicators acquire consequences.
Once a measure steers behaviour, it changes from an observation tool into part of the system.
An organisation selects a measurable indicator because it is associated with an important objective. Once bonuses, rankings or automation are tied to that indicator, actors discover ways to improve the figure without improving the underlying objective to the same extent.
Education, healthcare and performance management show gaming, tunnel vision and score inflation, but targets can also produce real improvement. These laws are therefore not a prohibition on measurement; they are warnings about feedback and design.
Optimisation pressure can make previously passive proxies part of the changing system. If actors exploit ways to improve the proxy without proportionate improvement in the objective, the relationship between proxy and objective can weaken. Whether this happens, and to what extent, depends partly on incentives, adaptation and independent checks.
AI transfer to investigate: AI does not create this mechanism, but increases the search power, speed and scale with which specification gaps and loopholes can be found. Reward hacking and specification gaming are direct technical relatives.
Proposed test, not yet conducted: Compare informative KPIs, human target pressure, AI optimisation against the same proxy, and AI optimisation with hidden or rotating independent audits. The main measure is the rate of proxy improvement versus independently measured improvement in the objective.
A metric must be reassessed once it becomes an intervention. Good measurement quality before optimisation pressure does not guarantee the same evidential meaning afterwards.
A proxy is a measurable stand-in for an objective. Optimisation pressure can change the relationship; deterioration is not inevitable. Measure the objective independently of the rewarded proxy.
Goodhart (1984), Monetary Theory and Practice; reprint of Problems of Monetary Management
Campbell (1979), Assessing the impact of planned social change
The passage on corruption pressure and independent checks comes from Campbell’s 1976 working paper (pp. 49–54), not the 1979 journal version. Bibliographic details and context are available for Goodhart’s chapter; its full text was not accessible. Deterioration is not inevitable.
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